There are known methods for improving the reliability of a storage controlling system including a plurality of storage apparatuses upon the occurrence of a failure and known methods for preventing a reduction in the performance of such a system. Japanese Laid-open Patent Publication Nos. 2005-339216 and 2008-242872 relates the known methods
FIG. 20 is a diagram schematically illustrating the configuration of a related-art storage controlling system.
Referring to FIG. 20, the related-art storage controlling system, indicated at 900, is a Redundant Arrays of Inexpensive Disks (RAID) system including arrays of storage apparatuses, for example. The storage controlling system 900 is connected to a host computer 901, serving as an upper-level apparatus.
The storage controlling system 900 performs processing, for example, reads or writes data from/to a storage apparatus (not illustrated) in accordance with an input or output request (e.g., a read command or a write command) from the host computer 901. In some cases, such an input or output request is also called “I/O command”.
Referring to FIG. 20, the storage controlling system 900 includes control modules (hereinafter, “CMs”) #00 and #01 and expanded enclosures DE#001 and DE#002. The CMs #00 and #01 are connected to the host computer 901. The CMs #00 and #01 are connected in series to the expanded enclosures DE#001 and DE#002. Specifically, as illustrated in FIG. 20, the CMs #00 and #01 are connected to the expanded enclosure DE#001, and the expanded enclosure DE#001 is connected to the expanded enclosure DE#002. The CMs #00 and #01 are received in an enclosure DE#000.
The CMs #00 and #01 perform various controls in the storage controlling system 900. The CMs #00 and #01 control access to the storage apparatuses included in the expanded enclosures DE#001 and DE#002 in accordance with I/O commands transmitted from the host computer 901.
The CM #00 includes a RAID-On-Chip (RoC) 801a and a back end expander (BE-EXP) 802a. The CM #01 includes a RoC 801b and a BE-EXP 802b. 
The RoCs 801a and 801b perform various controls in the CMs #00 and #01, respectively. The RoCs 801a and 801b each include two interfaces DI#00 and DI#01. In the RoC 801a, the interface DI#00 is connected to the BE-EXP 802a via a data path 811a. In addition, the interface DI#01 is connected to the BE-EXP 802b in the CM #01 via a data path 812a. 
In the RoC 801b, similarly, the interface DI#00 is connected to the BE-EXP 802b via a data path 811b. In addition, the interface DI#01 is connected to the BE-EXP 802a in the CM #00 via a data path 812b. 
In other words, in the related-art storage controlling system 900 in FIG. 20, the RoC 801a in the CM #00 is connected to the BE-EXP 802b in the other CM #01 through the interface DI#01 and the RoC 801b in the other CM #01 is connected to the BE-EXP 802a in the CM #00 through the interface DI#01 (cross connection).
The BE-EXPs 802a and 802b are connected to one or more common storage apparatuses (not illustrated) and control access to the storage apparatuses in accordance with disk access commands transmitted from the RoCs 801a and 801b. Since each of the BE-EXPs 802a and 802b is connected to the one or more storage apparatuses, an access path to each storage apparatus is duplicated.
Each of the expanded enclosures DE#001 and DE#002 includes one or storage apparatuses (not illustrated) and expanders (EXPs) 803a and 803b such that the EXPs 803a and 803b are connected to the one or more storage apparatuses to duplicate an access path to each storage apparatus.
The EXPs 803a and 803b control access to the storage apparatuses in accordance with disk access commands transmitted from the RoCs 801a and 801b. 
The EXP 803a in the expanded enclosure DE#001 is connected to the BE-EXP 802a in the enclosure DE#000 via a data path 813a-1. The EXP 803a in the expanded enclosure DE#0002 is connected to the EXP 803a in the expanded enclosure DE#001 via a data path 813a-2.
Similarly, the EXP 803b in the expanded enclosure DE#001 is connected to the BE-EXP 802b in the enclosure DE#000 via a data path 813b-1. The EXP 803b in the expanded enclosure DE#002 is connected to the EXP 803b in the expanded enclosure DE#001 via a data path 813b-2.
In the enclosure DE#000, the RoCs 801a and 801b each have a monitoring function of monitoring whether a system abnormality has occurred in the storage controlling system 900. When detecting the occurrence of the abnormality in any of the EXPs 803a and 803b, the RoC 801a or 801b disconnects the relevant EXP 803a or 803b. For example, if an abnormality is detected in either of the CMs #00 and #01, the other CM disables the CM in which the abnormality has been detected.
FIGS. 21 to 23 are diagrams explaining a process of recovering the disabled CM #00 in the related-art storage controlling system.
For example, if the CM #00 is disabled for any reason, the EXPs 803a in the expanded enclosures DE#001 and DE#002 connected to, or under the interface DI#00 of the CM #00 are also disabled.
The disabled CM #00 or #01 and the EXPs 803 are recovered by a process of incorporating into the storage controlling system.
In the related-art storage controlling system 900, when the CM #00 is recovered from the disabled status, the EXP 803a in the expanded enclosure DE#001 is subjected to the incorporating process (refer to FIG. 22). After the EXP 803a in the expanded enclosure DE#001 is recovered, the incorporating process on the EXP 803a in the expanded enclosure DE#002 is started (refer to FIG. 23). At the completion of the incorporating process on the EXP 803a in the expanded enclosure DE#002, the storage controlling system 900 enters the normal status.
The process of incorporating an EXP into the related-art storage controlling system will now be described with reference to a flowchart (including A10 to A120) illustrated in FIG. 24.
The process of incorporating the EXP 803a is performed by the CM which is not disabled. In the following description, it is assumed that the CM #01 which is not disabled performs the process of incorporating any EXP 803a under the disabled CM #00.
To incorporate the EXP 803a, the CM #01 reboots the EXP 803a to be incorporated (A10). If only the CM is to be incorporated, this EXP 803a is not rebooted.
The CM #01 starts a timer (EXP READY monitoring timer) for monitoring whether an EXP READY notification has been transmitted (A20). The EXP READY notification is information indicating the completion of boot-up of the EXP 803a. 
The CM #01 determines whether the EXP READY notification has reached for a predetermined time (A30). If the EXP READY notification has not reached the CM #01 for the predetermined time (NO in A30), the incorporation of the EXP 803a is interrupted (A40). The process is terminated.
If the EXP READY notification has reached the CM #01 for the predetermined time (YES in A30), the CM #01 changes an EXP status indicating the status of the EXP 803a (A50). In addition, the CM #01 cancels the EXP READY monitoring timer (A60).
After that, the CM #01 sets DEID related to the EXP 803a, time-of-day (TOD), and the model type of CM (hereinafter, “CM model type”) (A70 to A90). The DEID is information for identifying the expanded enclosure on which the EXP 803a is mounted.
In addition, the CM #01 acquires the World Wide Name (WWN) of the EXP 803a and the version number of firmware (“Firm Version Number”) (A100 and A110).
After that, the CM #01 sets the EXP status indicating the status of the EXP 803a to “ONLINE” (A120).
In the storage controlling system in which the RoCs are cross-connected to the BE-EXPs, however, the system cannot be recovered in some cases during, for example, incorporation of the CM #00, as will be described below.
FIG. 25 illustrates a status during recovery of the CM #00 in the related-art storage controlling system 900. In the case illustrated in FIG. 25, the incorporation of the CM #00 is completed but the EXP 803a in the expanded enclosure DE#001 and the subsequent EXP 803a have not yet been recovered. Referring to FIG. 25, the CM #00 has been disconnected and then incorporated while an abnormality occurred in the interface DI#01 (on the INPUT side of the BE-EXP 802b in the CM #01) in the CM #00 is not removed.
In the storage controlling system, when the incorporation of the CM #00 is completed, a disk access from the host computer 901 to a storage apparatus under the CM #00 may occur.
As shown in FIG. 25, however, the expanded enclosures DE#001 and DE#002 are recovered after the completion of the incorporation of the CM #00 in the related-art storage controlling system. Accordingly, even if the incorporation of the CM #00 is completed while the interface DI#01 in the RoC 801a has the abnormality, a disk access from the host computer 901 may occur, regardless of the absence of an access path from the CM #00 to the expanded enclosure DE#002.
Consequently, all of access to the expanded enclosure DE#002 result in errors, finally leading to disk abnormalities. Disadvantageously, the CM #00 cannot be incorporated into the system and the storage controlling system 900 cannot be recovered.
FIG. 26 is a diagram explaining a host I/O command and broadcasts (BCs) in the related-art storage controlling system.
In the storage controlling system 900, after the incorporation of the CM #00 is completed, the BE-EXP 802a and the EXPs 803a under the CM #00 are sequentially incorporated into the system. Each time the component is incorporated, a broadcast is performed in order to acquire information from an interface chip (not illustrated). A broadcast signal is output to a route (data paths 811a, 813a-1, and 813a-2).
Furthermore, after the CM #00 is incorporated into the storage controlling system 900, a host I/O command is transmitted through a straight route from the RoC 801a to the EXP 803a in the expanded enclosure DE#002, so that the system operates. Accordingly, at the completion of the incorporation of the CM #00 into the related-art storage controlling system 900, broadcasts are performed on the same route as that the host I/O command is transmitted through.
Consequently, even if the interface DI#01 has no abnormality as described above, a host I/O command is affected by the broadcasts performed during incorporation of the EXPs 803a. Disadvantageously, the performance of the system is deteriorated.